From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D8DA4338596 for ; Tue, 6 Jan 2026 19:20:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767727256; cv=none; b=cbX1ujwrNfQYE+EYBMsDOZZ39/Pj3CuevjXs549LJuXfgowBeSdivandeIpApbQvZxxYFb3D1D49FqNqCbP2CNSjOosPuWTfNQpr1UF56TidjVUGzKXZNVQERQiMSh71PxG38hlp/+HHAXNJJo4OHHcftWkH56LR8xMz7IGFMo0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767727256; c=relaxed/simple; bh=eo/x9ROfg5WKQWxp7LBJD1JrVmKZnu+ytyd9m+qhnzk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=G11u9HYrtfZR/ydy+zB5tylcPGPFmEdKNcpGjo5gVNWBP8gCQI57mzTrr6+iggiN7+KZfmwDRR1LLxm2jUcI3thzzj+aie3vRetsfBHZWZ6hEe80yFq2Ncc9UkPHBoM2bi++jD4yVScNTXWdIKJe0r7YH3jyYh/XIfoL0HYtE1c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IADNriuX; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IADNriuX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7AD41C116C6; Tue, 6 Jan 2026 19:20:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767727256; bh=eo/x9ROfg5WKQWxp7LBJD1JrVmKZnu+ytyd9m+qhnzk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=IADNriuXuMloqcnP3VojVv6eQPZ5CHvGqQzSUV+rWO64RTnJGVw2B7FdiFpkgwwRn vGIFwEFMXWPfG4EwUm3YSQ1F9EwCGpvmzfqvLcCBlc8IUflqm4/Asqy8AKrOT9njPg kDSBOec2TPZ6CH4av7XEgso2iYXcPZekt9xWsYvAN3smKhB7qlvNCsSO8bcZ4PzJ5i P4eJ9qxqwLVCpiEd65ASVxjg36sb84JgGb2qVsdc4ItNRPf5wlugCPO1Pokkw5Lg1u l36EP5PCLRiC83Jn7PMmBhpahXspun1ZrPqjN7WAQYq4aF7wFLZiKFTGRW5wfJgvko xsnZqjxD0YoGg== Message-ID: <9e8b01f9-d1b0-44a7-86c9-97622b2baec1@kernel.org> Date: Tue, 6 Jan 2026 20:20:51 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7] page_alloc: allow migration of smaller hugepages during contig_alloc To: Zi Yan Cc: Gregory Price , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, vbabka@suse.cz, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, richard.weiyang@gmail.com References: <20251221124656.2362540-1-gourry@gourry.net> <9c807ff8-b4ad-43d5-8034-ec7fcd0fe5d6@kernel.org> <36001B4C-A781-4571-AE65-4C00C9D215FC@nvidia.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/6/26 19:56, Zi Yan wrote: > On 6 Jan 2026, at 13:46, David Hildenbrand (Red Hat) wrote: > >>> - return false; >>> + /* >>> + * Only consider ranges containing hugepages if those pages are >>> + * smaller than the requested contiguous region. e.g.: >>> + * Move 2MB pages to free up a 1GB range. >>> + * Don't move 1GB pages to free up a 2MB range. >>> + * >>> + * This makes contiguous allocation more reliable if multiple >>> + * hugepage sizes are used without causing needless movement. >>> + */ >>> + if (PageHuge(page)) { >>> + unsigned int order; >>> + >>> + if (!IS_ENABLED(CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION)) >>> + return false; >>> + >>> + if (skip_hugetlb) { >>> + *skipped_hugetlb = true; >>> + return false; >>> + } >>> + >>> + page = compound_head(page); >>> + order = compound_order(page); >>> + if ((order >= MAX_FOLIO_ORDER) || >>> + (nr_pages <= (1 << order))) >>> + return false; >>> + >>> + /* >>> + * Reaching this point means we've encounted a huge page >>> + * smaller than nr_pages, skip all pfn's for that page. >>> + * >>> + * We can't get here from a tail-PageHuge, as it implies >>> + * we started a scan in the middle of a hugepage larger >>> + * than nr_pages - which the prior check filters for. >>> + */ >>> + i += (1 << order) - 1; >> >> Assuming page != compound_head(page), you'd be skipping too much. > > It might not happen based on my reasoning[1], but feel free to punch poles. :) :) hehe, I should just have read that comment more carefully. Anyhow, I wonder whether removing 6 lines of comments by just doing it properly might be better? head = compound_head(page); order = compound_order(head); ... i += (1 << order) - 1 - (page - head); In any case Acked-by: David Hildenbrand (Red Hat) -- Cheers David